Thanks, Nuance have confirmed that it definitely isn't possible with their software. Their response:

Subject

Is it possible to retain comments
when converting PDF to .docx?

Discussion Thread

"No, unfortunately, since Microsoft Word and Power PDF use
different ways of organizing and administrating comments, it is not possible to
convert and export the PDF to a Word document keeping the comments and its
owner. You can, indeed, import and export comments file onto PDF's, but not on
Word."

Thanks, Nuance have confirmed that it definitely isn't possible with their software. Their response:

Subject

Is it possible to retain comments
when converting PDF to .docx?

Discussion Thread

"No, unfortunately, since Microsoft Word and Power PDF use
different ways of organizing and administrating comments, it is not possible to
convert and export the PDF to a Word document keeping the comments and its
owner. You can, indeed, import and export comments file onto PDF's, but not on
Word."